1. Field of the Invention
The present invention relates to a map generation device which generates a road map used by a navigation device in response to the needs of a user.
2. Description of the Related Art
FIG. 1 is a block diagram of a navigation device including a conventional map generation device which generates a road map and which is disclosed for example in JP-A-6-137881. In the figure, reference numeral 10xe2x80x2 denotes a road map data storage section for storing road map data containing roads, place names, building names and rivers, 14xe2x80x2 is a GPS receiver which uses GPS to measure a present position of the vehicle, 16xe2x80x2 is a bearing sensor for detecting a direction of travel of the vehicle based on geomagnetism, 17xe2x80x2 is a steering sensor for detecting variation in a direction of motion by the operational angle of a steering wheel, 18xe2x80x2 is a distance sensor for detecting a running distance by the number of rotations of the vehicle wheels, 12xe2x80x2 is a present position measurement section which estimates a present position of the vehicle based on a detection result of the above sensors.
19xe2x80x2 is an input section which sends a destination input by a user to the calculation section 20xe2x80x2, 22xe2x80x2 is a route calculation section which is provided in the calculation section 20xe2x80x2 and which stores a route from the present position calculated by the present position measurement section 12xe2x80x2 to a destination, 24xe2x80x2 is a route storage section which stores the route calculated by the route calculation section 22xe2x80x2, 26xe2x80x2 is a route guide control section which is provided in the calculation section 20xe2x80x2, which reads road map data in the periphery of the vehicle from the road map data storage section 10xe2x80x2, which superimposes the route stored in the route storage section 24xe2x80x2, the present position of the vehicle and the direction of travel of the vehicle on the road map data and which displays the result on the display section 28xe2x80x2. 10a is a road rank storage section for storing ranks which are applied to roads, 22a is a road rank changing section which changes the rank of a road.
The operation of the conventional map generation device will be described below.
A navigation device including this type of conventional map generation device can select, based on a road category, roads to be displayed in accordance with a scale of the display screen. A rank is applied to each road in accordance with its road category and the rank applied to each road is stored in the road rank storage section 10a. Thus, if a display of detail up to roads with narrow width is performed, the screen may become crowded with information and difficult to understand. In such a case, low rank roads are omitted from the display and only arterial roads may be displayed.
Furthermore, when a destination is input from the input section 19xe2x80x2 by a user, the route calculation section 22xe2x80x2 can perform route search to the destination using only main roads and arterial roads above a fixed rank as a search object. Thus, it is possible to reduce route searching time. However, when the route search is performed using only arterial roads as a search object, it is sometimes not possible to guide a route to the destination. In order to solve this problem, when a destination is input, the route calculation section 22xe2x80x2 changes the rank of roads in the proximity of the destination by the road rank changing section 22a prior to the route searching so that those roads become search objects for the route search. In such a way, even when the rank of roads in the proximity of the destination is not as high as an arterial road, it is possible to guide a route to the destination.
Since the conventional map generation device is constructed as above, it is necessary for the calculation section 20xe2x80x2 to read large amounts of map data during route searching, as a result, a large capacity memory must be provided which creates a high load on the hardware.
The present invention is proposed to solve the above problem and has the object of providing a map generation device which can limit road map data extracted from a road map data storage section, when searching a route, to that data required for needs of a driver. Thus, it is possible to perform high speed searching of a route and reduce the capacity of a memory by providing an optimal road map for the needs of the driver.
The map generation device of the present invention comprises an arterial road extraction means for extracting only arterial roads from the road map data stored in the road map storage means in accordance with a fixed determination standard and for generating information on a road network composed of the arterial roads as optimal road network information, and an optimal map storage means for storing the optimal road network information generated by the arterial road extraction means.
In such a way, as well as enabling high speed searching of a route, the capacity of a memory required to search the route can be reduced.
According to the present invention, the arterial road extraction means may be adapted to use a road category such as national road, prefectural road or the like as the fixed determination standard.
In such a way, as well as enabling high-speed searching of a route, the capacity of a memory required to search the route can be reduced.
Further, according to the present invention, the arterial road extraction means may be adapted to use a road width as the fixed determination standard.
In such a way, as well as enabling high-speed searching of a route, the capacity of a memory required to search the route can be reduced.
Furthermore, according to the present invention, the arterial road extraction means may be adapted to use both a road category such as national road, prefectural road or the like and a road width as the fixed determination standard.
In such a way, as well as enabling high-speed searching of a route, the capacity of a memory required to search the route can be reduced.
A map generation device of the present invention comprises a road map storage means for storing road map data, a point database storage means for storing information about the positions of a plurality of predetermined points, an optimal road network information generation means for extracting a road network composed of roads connecting the plural points from the road map data stored in the road map storage means according to the information stored in the point database storage means and for generating information about the road network as optimal road network information, and an optimal map storage means for storing the optimal road network information obtained by the optimal road network information generation means.
In such a way, as well as enabling high-speed searching of a route with respect to the predetermined points, the capacity of a memory required to search the route can be reduced.
A map generation device of the present invention comprises a road map storage means for storing road map data, a traffic flow database storage means for storing information relating to the traffic flow on the road and/or geographical points, an optimal road network information generation means for extracting a road network from the road map data stored in the road map storage means in accordance with the information stored in the traffic flow database storage means and for generating information about the road network as optimal road network information, and an optimal map storage means for storing the optimal road network information obtained by the optimal road network information generation means.
In such a way, as well as enabling high-speed searching of a route, the capacity of a memory required to search the route can be reduced.